Electrical switch and variable resistor for miniature electrical apparatus



March 7", 1950 R WOLFF ETAL 2,499,711

ELECTRICAL sw H AND VARIABLE RESI R FOR MINIATURE ELECTRICA APPARATU Filed Jan. 7, 48

IN V EN TORS ROBERT L. WOLFF BY HENRY J-GLUECKSTEIH m wk FIQS W M ATTORNEY Patented Mar. 7, 1950 ELECTRICAL SWITCH AND VARIABLE RE- SISTOR FOR MINIATURE ELECTRICAL APPARATUS Robert L. Wolf! and Henry J. Glueckstein, Milwaukee, Wis., assignors to Globe-Union Inc.,

Milwaukee, Wis., a corporation of Delaware Application January 7, 1948, Serial No. 1,014

7 Claims.

This invention relates to improvements in electrical switches incorporated with variable resistors and especially designed and adapted for use in connection with miniature electrical apparatus such as hearing aids and pocket receivers.

Assemblies of this type of necessity must occupy a minimum of space yet the switch must be self-cleaning because in many applications of miniature electrical apparatus dust, lint, hair, deposits from perspiration, and other foreign substances, due to the carrying of the device by people, collect on the switch and cause the malfunctioning of the butt or pressure contact type of switches.

It is an object of this invention, therefore, to provide a switch and variable resistor assembly wherein the switch is self-cleaning and so assembled directly to the variabl resistor that a minimum of space is required for the unit.

It is a further object of the invention to provide a switch and variable resistor assembly. the action of which is characterized by a distinct feel which indicates the off position of the switch.

A still further object is to provide a self-cleaning switch mounted on and operated by a variable resistor in which the switch is electrically quiet during the operation of the resistor.

These objects are attained by providing a base in which is rotatably mounted an operating shaft. One side of the base supports a variable resistor of a conventional type controlled by the rotation of the shaft, such rotation being controlled by a knob secured thereto. On the opposite side of the base within the periphery thereof is flatly positioned a pair of spaced terminals. A switch blade is mounted on one of these terminals and is spring-biased toward and into wiping engagement with the other terminal to make electrical contact therewith. A cam carrying member, directly mounted on the operating shaft, in one position thereof has a cam or tooth which engages a cam follower on the blade and holds it in "open position. In the other positions of the cam carrying member it is out of contact with the switch blade assembly and will not disturb the switch as the cam carrying member rotates during operation of the variable resistor. A slight lost motion connection between the cam carrying member and the shaftpermits th cam carryingmember to move relative to the shaft as the cam rides past the switch to provide a distinct feel to the movement of the knob thus indicating that the switch has been operated to either its open or closed positions.

The electrical switch so constructed and incorporated with the variable resistor may be of extremely small size. The switch and resistor unit herein shown, exclusive of the knob, terminals and mounting studs, has an overall diameter of approximately .615 to .619 inch, and an overall approximate thickness of approximately .351 inch. In spite of such small size, the switch so incorporated with the unit has a wiping action which removes from the contacting surfaces any dust, lint, or other foreign substance which would be detrimental to the establishment of a positive electrically noiseless contact. As the switch is spring-biased to its closed position, and in such position the switch blade assembly is out of engagement with the cam as it rotates during regulation of the variable resistor, the electrical contact will not be disturbed, thus keeping the switch as electrically quiet as possible.

The novel features, which are considered characteristic of the invention, are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawing, in which:

Fig. 1 is a view in side elevation of a variable resistor and incorporated switch embodying the present invention;

Fig. 2 is a plan view of the switch of Fig. 1;

Fig. 3 is a plan view of the switch of Fig. 1 with the variable resistor rotated from the off position;

Fig. 4 is an enlarged fragmentary sectional view taken on line 4-4 of Fig. 3;

Fig. 5 is a fragmentary enlarged view in side elevation taken from line 55 of Fig. 3;

Fig. 6 is a plan view of the terminal which supports the switch blade; and

Fig. 7 is an enlarged fragmentary plan view of the cam for operating the switch.

Referring to the drawing by reference numerals, the switch is mounted on and incorporated with a small variable resistor especially adapted for use in connection with miniature electrical apparatus such as hearing aids and pocket receivers. The resistor is of conventional design. It is mounted on one side of the base member ID and is enclosed by said member and a sealing cover 8. The knob II is fixed to an operating shaft l3 by means of a screw 9. The shaft I3 is rotably mounted in the base I!) so that upon rotation of the knob H with respect to the base If) the shaft l3 regulates the variable resistor.

The base H1 is made of insulating material and forms a support for the variable resistor terminals l2 and the switch terminals l4 and I5. A semi-circular raised portion i6 is formed on the base Ill about the operating shaft l3 to provide a fixed positioner engageable with the terminals l4 and I5 to locate them and aid in holding them in fixed position. The terminal H is Secured to the base by a rivet l1 and a mountingv stud I8. The terminal I! is secured to the base ID by the mounting stud l9 and the switch blade pivot pin 20. In some installations it may be desirable to mount the unit by laterally extending mounting arms 2| and 22 formed integrally with the terminals [4 and [6 as shown in the broken lines of Fig. 2. In such case the mounting studs l8 and I9 are replaced by rivets similar to rivet l1. Stops 23 raised from the face of the terminals l4 and I6 engage the hexagonals on the studs I3 and I3 to prevent them from rotation when nuts are threaded thereon in the mounting of the unit.

The terminal l6, as shown in Fig. 6, has an upright abutment 24 formed integrally therewith adjacent the pivot pin 20. This abutment has a notch 25 which engages and positions the one end of the switch spring. Except for this abutment the terminals l4 and I are fiat and rest on the back of the base I6 adding only a nominal amount to the thickness of the unit. A switch blade 26 is swingably mounted on the pivot pin 20. It has 9. turned down lip 21 which is slightly rounded and which is in overlapping relationship with a fixed contact 26 integral with the terminal 14. The switch blade 26 is held against a flange 29 on the pivot pin and urged into lateral and abutting engagement with the fixed contact 28 by a coil spring 30, the coils of which fit over the pivot pin 20 and are held thereon by a washer 3| staked or riveted to the top of such pin. The top end of thecoiled spring 30 rests and is held in the notch 25 while its lower end rests on the surface of the blade 26 and reacts against a cam follower 32 mounted on such blade. The cam follower in this embodiment is in the form of a pin riveted to the blade 26. In lieu of this construction the blade 26 may have an integral portion thereof bent upwardly to function as the cam follower. The blade 26 is also provided with a rear projection 33 which strikes against the abutment 24 to limit the extent that the blade 26 may be swung inwardly. With this organization of parts, the blade 26 is continually urged into closed position. In moving into closed position the lip 21 strikes against the fixed contact 28 and rides up and along its surface for an appreciable distance thus producing a wiping action between the lip and contact which will clean the contacting areas and secure a good electrical connection therebetween even though dust, lint and other foreign substances are present.

The switch is moved from its closed position to open position by a cam carrying member 34. The cam carrying member 34, preferably made of fibrous insulating material, is mounted on the operating shaft I3, and, as is shown in Fig. 2, there is a slight lost motion connection between the cam carrying member and the shaft. This is accomplished by making an oblong slot in the cam carrying member which is slightly oversize with respect to the oblong end of the shaft l3 on which it fits. The cam carrying member 34 is held on the shaft by a hexagonal headed bolt 35 which threads into the end of the shaft l3. The cam carrying member 34 has a notch 36 defined by two spaced cams or teeth 31 and 38. The distance of the bottom of notch 36 from the rotational 'axis of cam carrying member 34 is sumcient to keep blade 26 open when cam follower 32 rests in the notch 36. Two cams or teeth are provided so that the cam carrying member 34 may be alternately used to operate the switch at the selected end of either a clockwise or a counter-clockwise rotatable variable resistor. Since the follower 32 moves in an are about the switch pivot, the clockwise leading edge of cam or tooth 38 is arcuate (see Fig. 7) to prevent hooking the follower. The sloping slides oi the cams or teeth cooperate with the cam follower 32 not only to open the switch but also to cause the cam carrying member 34 to advance with respect to the shaft I3 the amount permitted by the lost motion connection as the cam follower 32 passes over the peak of a tooth. This has two effects. It imparts a definite feel to the operating shaft l3 and knob ll, making the operator aware of the movement into orout of open position, and provides a semi-snap action in the closing of the blade 26. The longer axis of the oblong end of the operating shaft I3 is so alined with the variable resistor operating mechanism that the notch 36 of the cam carrying member is brought into contact with the cam follower 32 at the desired position of rotation. The other portions of the cam carrying member 34 are not in contact with the cam follower 32 when the blade 26 is forced by the spring 30 into its closed position as limited by the engagement of projection 33 with abutment 24. This insures that there will be no rotational torque drag on the shaft and no movement of the switch blade 26 as the shaft I3 is further rotated in the actuating of the variable resistor. The latter prevents any change in contact resistance in the switch and lessens the electrical noises that may be set up in the electrical circuit.

In the operation of the switch the knob II is rotated in either a clockwise or counter-clockwise direction dependent upon the construction of the variable resistor. Starting from the position shown in Fig. 2, as clockwise rotation commences, the lost motion connection is taken up, if not absorbed up to this time, and the cam carrying member 34 commences to rotate, causing the cam follower 32 to ride up to the peak of the cam or tooth 31. As soon as the high spot of the tooth passes the high point of the cam follower 32 the pressure of the spring 30 will force the blade 26 inwardly causing the cam carrying member 34 to advance in the direction of its rotation the amount permitted by the lost motion action.

This movement takes place rapidly and the blade 26 snaps into closed position. During the closing, the wiping action previously described takes place making a positive, firm, electrical contact between the blade 26 and the fixed contact 23.

. Continued rotation of the knob ll adjusts the variable resistor to the desired resistance. During such rotation the cam carrying member 34' is out of engagement with the follower 32 and the blade 26 is not disturbed. When it is desired to open the switch, the cam carrying member is rotated counter-clockwise and the sloping side of the cam or tooth 31 is brought into contact with the cam follower 32. If the lost motion connection is not prior to this time absorbed in reversal of movement it will be absorbed at the time of such contact. Further rotation causes the cam follower 32 to ride up the side of the cam or tooth 31 thus moving the blade 26 outwardly and disengaging it from the contact 23. As the high point of the cam or tooth 31 passes under the high point of the cam follower 32, the spring 30 will again force the cam follower 32 rapidly down the notch side of the cam or tooth 31. Thisthe cam follower to snap into the notch 36 imparting a definite feel to the knob H indicating that the switch has been moved to open position. With a reversely operating variable resistance, the switch is closed upon counter-clockwise rotation from the position shown in Fig. 2. The action is similar to that described, only in this instance the cam or tooth 38 is the operatin tooth. In opening the switch the arcuate sloping side of the cam engages the follower 32 upon clockwise rotation and because of its curvature lessens any binding action therebetween or hooking of the follower.

Although only one embodiment of the invention is shown and described herein, it will be understood that this application is intended to cover such changes or modifications as come within the spirit of the invention or scope of the following claims.

We claim:

1. An electrical control device including an insulating base, a shaft rotatably carried by said base, a fixed contact positioned on said base adjacent said shaft, a pivot pin mounted on said base and spaced from said shaft and said fixed contact, a switch blade loosely pivoted on said pin and swingable in the plane of said base toward said shaft to closed position, said blade being swingable outwardly with respect to said base upon engagement with said fixed contact to ride up and along said fixed contact and swingable away from said shaft to open position out of engagement with said fixed contact, a camcarrying member mounted on said shaft and having a cam positively engageable with a part of said switch blade for a small portion of the total rotational movement of said shaft to move said switch blade to open position, and spring means for continuously urging said switch blade toward said shaft and inwardly toward said base into closed position in engagement with said fixed contact.

2. An electric device as claimed in claim 1 in which said spring means consists of a coil spring mounted on said pivot pin and having an arm continuously urging said switch blade toward said base and toward said shaft whereby said blade engages said fixed contact with a wiping action.

3. A switch adapted to be attached to the base of a variable resistor adapted for use in connection with miniature electrical apparatus and operated by the rotatable member of said variable resistor extending from the base the eof, said switch comprising a pair of terminals one of which is fiat and rests against said base to provide the fixed contact for the switch, the other of said terminals being provided with a pivot pin and an abutment, a switch blade mounted on said pivot pin, said blade having a turned-down lip in overlapping relationship with said fixed contact swingable into wiping engagement over said fixed contact in the on position of said switch, a coiled spring mounted on said pivot pin and reacting between said blade and said abutment at an angle to the plane of pivotal travel of said blade to resiliently urge said blade forwardly and downwardly into on position, said switch blade having a projection engageable with said abutment to determine the on" position of said blade, a cam carrying member mounted on said rotatable member and having a cam positively engageable with said switch blade only during a small portion of the total rotational movement of said member to move said switch blade to open posi-v tion, said cam carrying member and cam being out of contact with said switch blade during the other portion of said movement so that durin the adjustment of the variable resistor there will be no disturbing movement imparted to said blade to cause electrical noise in the electrical circuit in which said variable resistor is connectible.

4. A switch as defined in claim 3 in which there is a lost motion action between said cam carrying member and said rotatable member to permit said cam carrying member to rapidly advance as said cam passes by its center of positive action with said blade to provide a distinct feel to the movable member to indicate the on or off position of said switch.

5. A switch as defined in claim 3 in which the cam carrying member has a notch between two spaced cams, said notch acting positively on said switch blade to keep it open,'one of said cams being active when said switch is employed to open the switch at one extreme of travel of a variable resistor and the other of said cams being employed to open the switch at the other extreme of travel of a variable resistor.

6. A switch as defined in claim 3 in which the switch blade has a cam follower and the cam has an arcuate edge for engaging the follower, the arcuate edge being sloped to approximate the path of the follower during pivoting of the blade to lessen frictional resistance between the cam and follower.

7. In an electrical control device including a variable resistor operated by a rotatable control shaft and a switch consisting of a fixed contact and a movable switch blade continuously springbiased toward on position, snap action simulating means for opening and closing said switch comprising a cam carrying member having a lost motion direct driving connection with said shaft, a cam follower on said blade, and a cam on said cam carrying member adapted to directly engage a cam follower on said switch blade and move said blade to off" position as said member is rotated by said shaft, said cam having a high point which passes by said cam follower and a sloping surface which after said high point passes is acted upon by said cam follower under influence of said continuously spring-biased blade to advance said cam carrying member with respect to said shaft for the limits of said lost motion connectlon to simulate a snap action.

ROBERT L. WOLFF. HENRY J. GLUECKSTEIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,171,596 Conrad et al. Feb. 15, 1916 1,557,207 Kroeger Oct. 13, 1925 1,708,225 Kroeger Apr. 9, 1929 2,090,347 Draving et al. Aug. 17, 1937 2,133,858 Hathorn Oct. 18, 1938 2,230,187 Meuer et a1 Jan. 28, 1941 2,314,714 Kouyoumjian Mar. 23, 1943 2,329,949 Shapiro Sept. 21, 1943 2,453,774 Basista Nov. 16, 1948 FOREIGN PATENTS Number Country Date 436,628 Great Britain Oct. 15, 1935 

